Vinylogous nucleophilic substitution

We also prepared poly(amide enamines) by vinylogous nucleophilic substitution. Poly(amide enamines) 8 were prepared from the reaction of diamines... 

A similar approach was described by Kim et al. <01MI1403> to build the Furstner synthon from the vinylogous amide 9, previously described, and the commercially available dimethyl aminomalonate hydrochloride as building block for pyrrole systems. The cyclocondensation reaction between the vinylogous amide 9 and dimethyl aminomalonate hydrochloride was performed in acetic acid at room temperature to yield the presumed Intermediate 12 via an acid-catalyzed nucleophilic substitution reaction. The mixture was then diluted with additional acetic acid and heated under reflux to facilitate the intramolecular ring closure and the loss of the methoxycarbonyl moiety to produce the desired pyrrole. Formation of lamellarin O dimethyl ether was achieved as in the Furstner approach <95JOC6637>. 

Activation of nucleophilic substitution of vinylogous carboxylic acids by 0-carbethoxylation... 

If vinylogous imidazole-A-carboxylates (route A) are treated with nucleophiles such as alkoxides or amines, the corresponding vinylogous carbonic esters or amides are obtained. While reaction of the vinylogous imidazole-TV-carboxylate with a thiol (route A) yields the addition product only, that of the corresponding imidazolium compound (route B) leads to the carbonic thioester in a substitution reaction [3]... 

Addition of carbon nucleophiles to furfural tosylhydrazone provides 5-substituted 2E,4E-pentadienyls in good yields <00TL2667>. The ab initio calculations at the RHF/3-21G level have been utilized to study the origins of diastereoselectivity of the vinylogous Mannich reaction of 2-methylfuran with pyrrolinium ion . A simple procedure for isomerization of 2-furylcarbinols to cyclopentenones under neutral condition was reported and a new mechanism was proposed <00H(52)185>. 

Chen and co-workers utilized the chiral bifunctional catalysts to directly access vinylogous carbon-carbon bonds via the asymmetric Michael addition of a,a-dicy-ano-olefms to nitro-olefms [102]. The scope of the reaction was explored with a variety of substituted a,a-dicyano-olefins and P-substituted nitro-olefms (Scheme 50). The authors propose the catalysf s tertiary amine functionality depro-tonates the cyano-olefm, activating the nucleophile to add to the -face of the pre-coordinated nitro-olefm. 

The acetyl-substituted complexes, initially prepared by Jager36 by direct synthesis, have served as the basis for all of the work in this area. It has been shown that the acetyl group can be replaced by substitution, especially nitration, where reaction conditions are rather vigorous.39 The acetyl-substituted complexes are not only nucleophilic at carbon, a property exhibited in the above reaction, but they are also nucleophilic at oxygen, being vinylogous amides, and undergo... 

The vinylogous elimination to give alkenylcyclopropanes may also be effected via rt-allyl palladium complexes34,35. The palladium(0)-catalyzed substitution of allylic esters with stabilized carbon nucleophiles via 7i-allyl palladium derivatives stereospecifically proceeds with net retention (double inversion) of configuration. Thus, the chirality of an allylic substrate is transferred to resultant alkenylcyclopropanes in the intramolecular S J/ reaction via 7i-allyl palladiums (equation 21)36,3. ... 

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